Link to what Xhi explains is here: http://www.howtogeek.com/howto.....ard-trick/
Maybe creating a new user account (and later deleting the old one if you want) fixes this. But as Santo says, I would absolutely go for a reinstall of the operating system. Take into consideration that Windows XP is 11 years old, and support and updates for it end in April 8, 2014. Consider upgrading to a newer Operating System, such as Windows 7 or Ubuntu 12.04.
You can install and test Windows 7 for free during 30 days with an ISO image from here. You will need to buy a license after that, so I would recommend getting the Home Premium version because it is cheaper:
Ubuntu is free, you can download the ISO image of Ubuntu Live CD from http://www.ubuntu.com/download/desktop . Select 12.04 LTS (32-bit version). Burn it to a CD, you can boot and test Ubuntu from this Live CD before installing.
Burn the ISO images with ImgBurn: